Plastic blow molding of containers is conventionally performed by providing a hot plastic parison either from extruded plastic or as a preform which is usually injection molded from plastic. Usually, such preforms are composed of a single type of plastic that is injected into a mold through a single port. However, there have also been attempts to provide conduction of more than one plastic into a mold so as to provide different layers of plastic.
U.S. Pat. No. 3,878,282 to Bonis et al. discloses a process for molding multi-layer articles that are specifically disposed as a preform-type parison with different layers. The process involved is performed by injection molding the different layers within different molds while mounted on the same inner mandrel during the injection of each layer.
U.S. Pat. No. 4,307,137 to Ota et al. discloses a method for forming an optical design pattern in polyethylene terephthalate articles which are specifically disclosed as a blow molding preform having inner and outer members with the inner member having an open end defining a thread closure and with the outer member having a junction with the inner member toward a closed end of the preform from the thread closure.
U.S. Pat. No. 4,391,861 to Nilsson discloses a preform of a thermoplastic and has a two-part interfitted construction and at least one intermediate layer that functions as a gas barrier, and also discloses that the outer part may be previously used and reprocessed material.
U.S. Pat. No. 4,646,925 to Nohara discloses a multi-layer preform for draw-blow forming a bottle which has inner and outer layers with a junction that is located toward a closed end of the preform from a closure thread at an open end of the preform. The preform also includes a gas barrier intermediate the inner and outer layers.
U.S. Pat. No. 5,102,705 discloses a bottle made of polyethylene naphthalate resin produced by highly stretching a preform in a manner that is disclosed as limiting gas permeability and x-ray transmission.
Reusable glass bottles for holding pressurized beverages have been substantially replaced by plastic blow molded bottles. Such plastic blow molded bottles were initially manufactured with a hemispherically shaped lower end so as to withstand the internal pressure involved, and this lower end was received within an injection molded base cup for supporting the bottle. More recently, such plastic blow molded containers have been manufactured with freestanding base structures such as disclosed by U.S. Pat. No. 5,064,080 Young et al, U.S. Pat. No. 5,139,162 Young et al and U.S. Pat. No. 5,287,978 Young et al.
U.S. Pat. No. 3,717,544 Valyl, U.S. Pat. No. 3,719,735 Valyl and U.S. Pat. No. 4,067,944 Valyl disclose multi-layer blow molded containers made from preforms having an inner layer provided by a liner about which an outer layer is formed by injection molding. The U.S. Pat. No. 3,717,544 Valyl patent discloses the liners as being made by a thermoforming process wherein a vacuum is applied to a female mold to deform a heated plastic sheet to the shape of the mold.
U.S. Pat. No. 5,443,766 Slat et al discloses a multi-layer preform used for plastic blow molding and provided with an inner layer of polyethylene naphthalate that is thermoformed to function as a gas barrier.
Thermoforming of liners for blow molding preforms is more easily performed in connection with making large mouth containers rather than spout type containers where a dispensing spout projects upwardly from an upper dome that extends upwardly and inwardly from the container body portion. This is because the ratio of the height of the preform over the open diameter is much smaller for large mouth preforms than is the case for spout type preforms. For many applications, spout containers cannot be thermoformed to provide a liner because the height of the preform is too great in comparison with the open diameter such that the material even when heated cannot be stretched enough to form the spout type preform liner.
The dominant gas barrier commercially utilized at the present time to prevent gas transmission through blow molded containers is polyethylene vinyl alcohol (EVOH) which may be dipped, sprayed or brushed as well as coinjected with plastic resin. One disadvantage of EVOH is that it must be fully enveloped by the plastic of the preform or it will tend to draw moisture from the atmosphere and thereby loses its ability to function in preventing gas transmission through the container.